feat: initial stats-cohort-size v0.1.0 (stats.cohort_size@0.1.0)

Resolve the size of an addressee cohort (e.g. "Berliner KMU",
"Gastronomie deutschlandweit").

v0.1.0 ships a five-entry built-in lookup for the F∆I Law-Heatmap
pilot corpus:

  berlin-kmu, de-kmu, gastro-de, handwerk-be, bauwirtschaft-be

Each entry carries (count, year, source, tier). Tier follows the
Studie §6.7 Regel-der-niedrigsten-Stufe: T1 when from DESTATIS
Unternehmensregister, T2 when from a Verband source.

Reuse-lens: any quantitative analysis that needs cohort sizing —
market research, audience targeting, public-health tracking.

Pure in-WASM, zero filesystem, zero network.

Reserved for next versions:

  - 0.2: DESTATIS GENESIS-API adapter — requires
         net: ["genesis.destatis.de"] permission. Interface stays
         the same; the static lookup becomes the fallback when
         the API is unreachable.
  - 0.3: WZ-Code-resolved sub-cohorts (e.g. "berlin-kmu-wz56").

Signed-off-by: flemming-it <sf@flemming.it>

Cargo.toml

@@ -0,0 +1,36 @@
+[package]
+name = "stats_cohort_size"
+version = "0.1.0"
+edition = "2024"
+authors = ["Dr. Stefan Flemming <chain@flemming.ai>"]
+license = "Apache-2.0"
+publish = false
+description = "F∆I module — resolve cohort sizes for addressee populations"
+repository = "https://git.flemming.ws/chain-modules/stats-cohort-size"
+rust-version = "1.85"
+
+[lib]
+crate-type = ["cdylib", "rlib"]
+
+[dependencies]
+chain-module-sdk = { git = "https://git.flemming.ai/fai/chain-module-sdk-rust.git", branch = "main" }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+
+[profile.release]
+opt-level = "s"
+lto = true
+codegen-units = 1
+strip = "symbols"
+
+[lints.rust]
+unsafe_op_in_unsafe_fn = "warn"
+
+[lints.clippy]
+unwrap_used = "deny"
+expect_used = "deny"
+panic = "deny"
+print_stdout = "deny"
+print_stderr = "deny"
+
+[workspace]